can't remove element from a list

[yokaso]

i have a list and i want to remove all non digit element from it,but got some problem.
there is my code , can you help me:

match = re.compile(r'ROL N°.[0-9][0-9].')

case_title = re.sub(match,'',expression) 
num_case= match.search(expression)

first_case_num=[]
 first_case_num = num_case.group()
 second_case_num=  num_case.group()
    
    for case in first_case_num:
        if case.isdecimal():
            pass
        else:
             first_case_num.remove(case)

---------------------------------------------------------------------------
AttributeError Traceback (most recent call last)
<ipython-input-91-521c272a0c4b> in <module>
27 print(case)
28 else:
---> 29 first_case_num.remove(case)
30
31

AttributeError: 'str' object has no attribute 'remove'